1. Field of the Invention
The present invention relates to golf clubs and, more specifically, a golf club head and weighting method to provide better performance, greater weighting flexibility and lower production costs.
2. Description of the Related Art
The location and distribution of weight within a golf club is an important factor in the performance of the golf club. In particular, weight placement at the bottom of the golf club head provides a low center of gravity to help propel a golf ball into the air during impact, and weight concentrated at the toe and heel of the golf club head provides a resistance to twisting, or high moment of inertia, during golf ball impact. Both the low center of gravity and high moment of inertia are important performance variables which affect playability and feel of the golf club. Alternative designs have resulted in many innovations for varying the weight location and distribution in a golf club head portion. Among these designs is a combination of high and low density materials within the golf club head, and associated methods for combining these materials.
One example of multiple materials used in the construction of the golf club head is a high density material attached to a lower density material golf club head. A high density block or contoured shape is attached, via mechanical means such as friction fit, fasteners or screws, to a reciprocal recess in the golf club head, as shown in U.S. Pat. No. 5,776,010, issued to Helmstetter et al. Although supplying the desired performance enhancements, the high density block and the reciprocal recess must be machined to precise tolerances, involving high production costs.
Another example of weighting the golf club is pouring a high density fluid into a reservoir within the golf club. This ensures an exact placement of the weighting material within the golf club, as the fluid will conform to the internal shape of the reservoir without the need for mechanical or an adhesive bonding. One drawback of this type of processing is the requirement that one must operate below the melt or softening temperature of the club head material. In addition, as processing temperatures increase the associated costs will increase to accommodate higher energy use and high temperature equipment. The limitations for a low melt temperature, yet high density, material restricts the available options for this type of process.
To overcome the limitations associated with a single material, the advent of multicomponent weighting systems makes use of the high density materials in combination with a carrier fluid, such as a polymer. A particulate form of the high density material is mixed with the carrier fluid and poured into the reservoir in the golf club, wherein the carrier fluid is allowed to solidify to form a composite weighting material. Readily available materials include a thermoset polymer carrier fluid, such as epoxy, which allows ambient temperature processing and solidification of the high density material and epoxy mixture. A thermoplastic polymer carrier fluid, such as polypropylene, requires heat to obtain a fluid state and cools to a solid at ambient temperatures, with the capability to be re-heated to the fluid state, in distinction to the epoxy. A disadvantage of the multi-component weighting system is the low density associated with the carrier fluid, typically 1 g/cm3, thus requiring a high ratio of the weighting material to the carrier fluid to obtain the desired high density for a bi-material weight. The carrier fluid also acts as a binder for the weighting material to ensure the bi-material weight forms a solid block.
A drawback to the multi-component weighting system is the need to use small amounts of carrier fluid relative to the weighting material, leading to entrapped air or voids and incomplete binding in the bi-material weight. Incorporating larger amounts of the carrier fluid promotes better mixing within the bi-material weight in conjunction with an attendant decrease in density. Therefore, it is desirable to provide a bi-material weight containing a higher density carrier fluid to provide greater weighting flexibility for allocating weight within a golf club head in conjunction with lower cost production. It is further desirable to provide a golf club head to accommodate the bi-material weight and enable a variable location of the bi-material weight.
The present invention addresses the problems of the golf industry by providing a bi-material weight and a golf club head that when used in combination result in a golf club that provides a low center of gravity, and superior feel and playability. A distinctive feature of the bi-material weight of the present invention is the use of vibrational energy to provide complete contact between the high density material and the lower density material. This embodiment reduces or eliminates voids associated with mixing dissimilar density materials, and promotes migration, or orientation, of the high and lower density materials to the preferred location within the golf club head.
In a preferred embodiment, the bi-material weight is a nonhomogeneous mixture composed of a high density metal material forming a discontinuous phase, and a lower density metal material forming a continuous phase. The choice of metal materials is advantageous for their high density, metal to metal compatability, availability and for many alloys good long term environmental stability. Among the choices for the high density metal material are copper metals, brass metals, steel and tungsten metals; wherein the lower density metals afford a low melt temperature and include several types of solder. In a most preferred embodiment, a plurality of tungsten spheres comprises the high density metal forming the discontinuous phase, and a bismuth-tin solder comprises the lower density metal forming the continuous phase. An important operation in achieving the nonhomogeneous mixture is providing the lower density material in a liquid state, followed by imparting vibrational energy to diminish or eliminate voids and permit migration of the high density metal material to a preferred location within the golf club head, followed by solidification of the lower density material.
A preferred embodiment of the present invention is generally descriptive of a class of golf clubs known as irons. Within this class is a type of iron referred to as a cavity back iron, and well known to those of ordinary skill in the art, which contains a continuous ribbon, or flange, of material at the outer periphery of the rear face of the iron. This construction yields an open cavity, or first cavity, in the rear or back of the iron and yields a larger xe2x80x9csweet spotxe2x80x9d in the front or striking face of the iron to provide a wider margin of error in striking the golf ball. The ribbon of material located below the open cavity, extending between the heel and toe and adjacent the bottom periphery of the golf club head, contains an internal cavity, also referred to herein as a second cavity or weight pocket, for accepting a weighting material. This cavity contains at least one inlet into an interior volume, or interior space, of the internal cavity, having a vertical dimension between a ceiling wall, or top wall, and a bottom wall, and a horizontal dimension between a toe region and a heel region of the golf club head. In a preferred embodiment, the internal shape, or configuration, of the internal cavity allows weight to be located in the toe region or heel region to help a golfer open or close the golf club head relative to the intended target line. Specifically, weight located in the toe region helps to open the golf club head, and weight located in the heel region helps to close the golf club head. In addition, an expanded center volume portion of the internal cavity allows for a vertical density transition zone in the bi-material weight, resulting in a more satisfying feel during golf ball impact.
In a preferred embodiment, an undercut recess is located rearward of a front face of the golf club, as discussed in U.S. Pat. No. 5,282,625, issued to Schmidt et al., which is hereby incorporated by reference. The purpose of the undercut recess is to help expand the xe2x80x9csweet spotxe2x80x9d, in conjunction with xe2x80x9csweet spotxe2x80x9d improvement inherent in the cavity back iron, by moving weight to a rearward peripheral region of the golf club head. In addition, the rearward location of the bi-material weight improves playability by helping propel the golf ball into the air during impact with the golf club.
Accordingly, it is an object of the present invention to provide a bi-material weighting system for golf clubs to allow a greater flexibility in locating the center of gravity and providing better feel.
It is another object of the present invention to impart vibrational energy to a bi-material weighting system for golf clubs to allow better mixing and orientation between the weighting materials to form a continuous phase and a discontinuous phase.
A further object of the present invention is to provide a golf club head containing an internal cavity having an expanded vertical dimension in the center of the cavity, thereby allowing greater precision in locating high density material in the center of the golf club head.
Another object of the present invention is to provide a cavity-back titanium alloy iron golf club head with a cavity containing a plurality of tungsten alloy spheres and a bismuth-tin solder.